Despite dramatic advances in curative combination chemotherapy for newly diagnosed patients with aggressive non-Hodgkin's lymphoma (NHL), few patients with relapsed B cell NHL can be cured with conventional treatments. The primary objective of this project is to investigate the therapeutic utility of high dose radiolabeled monoclonal antibodies targeting the CD20 antigen in conjunction with autologous stem cell rescue for treating patients with relapsed B cell lymphomas. In this application, we propose to perform long-term follow up of patients treated on prior phase I & II trials with IL-131-anti-CD20 antibodies+ASCT to ascertain long term efficacy and delayed toxicities (Aim 1), to conduct a phase II trial of I-131-anti-CD20 with etoposide (VP16), cyclophosphamide (CY) and ASCT to define toxicities and establish efficacy of this combined modality regiment for treating relapsed NHL (Aim 2), to extend the use of I-131-anti-CD20 + ASCT to elderly patients who have been excluded from prior trials of myeloablative radioimmunotherapy (Aim 3), and assuming favorable results in Aim 2, to conduct a randomized Phase II trial comparing I-131- anti-CD20+ VP16 + CY to external total body irradiation (TBI) + VP16 + CY (Aim 4). This sequence of trials should enable us to achieve our long term objective of establishing the role of high dose I-131-anti-CD20 + ASCT in the treatment of relapsed NHL.